1. Field of the Invention
The invention relates to a hydraulic unit for an anti-lock vehicle brake system.
2. Description of the Prior Art
A hydraulic unit of a vehicle brake system, which unit converts the commands of an electronic control unit and via valves controls the pressures in wheel brakes independently of a driver, is described for instance in German Published, Unexamined Patent Disclosure DE 44 31 250 A1.
This known hydraulic unit has a housing block, in which a first row of upper stepped bores and a second row of lower stepped bores are made for receiving multiposition valves; one upper stepped bore and one lower stepped bore each communicate with one another and additionally with a brake line connection bore. The upper stepped bores for receiving a multiposition valve also communicate with a wheel brake connection that also communicates with a low-pressure reservoir acting as a damper. From the low-pressure reservoir, a bore leads to a pump receiving chamber, which communicates with a further low-pressure reservoir and with two lower stepped bores that are intended to receive outlet valves.
For each of the two brake circuits provided, one so-called primary circuit is formed with line connections from a master cylinder, which predetermines the brake pressure, to the wheel brakes via the inlet valves inserted into the upper valve receiving chambers, while the line connections from the wheel brakes to outlet valves inserted into the lower valve receiving chambers, to the low-pressure reservoirs, and the return pump inserted into the pump receiving chamber, form a secondary circuit for return pumping into the primary circuit.
A disadvantage of the housing block of the hydraulic unit known from DE 44 31 250 A1, with a disposition of the pump receiving chamber between the valve receiving chambers and the low-pressure reservoirs, is that the secondary circuit of a brake circuit holds a large volume of pressure fluid, as a result this demarcated region, which is not flushed out in normal braking but rather only in braking with regulation of brake fluid, can be ventilated only with difficulty.
Moreover, when there is a relatively large enclosed volume of pressure fluid in the secondary circuit, there is the risk of outgassing of the enclosed volume, for instance if no regulation takes place over a relatively long period of time during cold weather.
From German Published, Unexamined Patent Disclosure DE 199 58 194 A1, a hydraulic unit for a traction-controlled brake system is known, with a receiving body that in a plurality of valve receiving bores in a first and second row of valves receives inlet valves and outlet valves and has a pump bore, disposed between the valve receiving bores and low-pressure reservoir receiving chambers, which is oriented transversely to the direction of discharge of the valve receiving bores into the receiving body and centrally forms a unit with a motor receiving bore, which is oriented perpendicular to the pump bore. Between these receiving bores or chambers, pressure fluid conduits connecting them with one another are made in the receiving body, which are capable of making a hydraulic communication between brake pressure transducer connections, that lead into the receiving body, and wheel brake connections, that lead away from the receiving body. Each two valve receiving bores for outlet valves are coupled in pairs by means of pressure fluid conduits and each communicate with a low-pressure reservoir receiving chamber via a respective return conduit.
Once again, there is the disadvantage of a large volume of pressure fluid in the secondary circuits of the vehicle brake system.
Furthermore, the connections among the individual receiving chambers in the receiving housing is disadvantageous in the sense that for the most part they have angles, rather than extending in straight lines. Thus the course of pressure fluid from two valve receiving chambers for outlet valves to the associated low-pressure reservoir receiving chamber is formed with a bore that initially connects the valve receiving chambers and with a further bore extending perpendicular to it; the latter bore is composed of two bore portions: A first of these bore portions is made from outside into the receiving housing, axially parallel to a longitudinal axis of the valve receiving chambers, and a second bore portion is made in the receiving housing axially parallel to a longitudinal axis of the applicable low-pressure reservoir receiving chamber, in the direction of the first bore portion. The transition region between the bore portions forms a 90° angle.
Besides the high engineering cost and the fluidic disadvantages of a 90° angle of this kind, another factor is that each bore portion must be closed off from the outside, for instance by a ball-like closure element. Thus there is also the risk of a possible leak during the operating time, since these closures are exposed to pressure pulsation.
German Published, Unexamined Patent Disclosure DE 44 06 269 A1 discloses a housing of an anti-lock brake system installed in a diagonal brake system with two brake circuits. In this housing, a pump receiving chamber is disposed between a first row of inlet solenoid valves and a second row of outlet solenoid valves; two solenoid outlet valves communicate with one another via a pressure line, which in turn communicates with a reservoir that forms a pulsation damper, which is exposed to high pressure and is connected downstream of the pump.
This known arrangement is already intrinsically complicated because of its design with dampers. Moreover, once again there are the disadvantages of a course of pressure fluid via a conduit connecting the outlet solenoid valves, and a pressure fluid conduit branching off from it to the reservoir, with corresponding twists and turns.